Nutritional Psychiatry

A research field built around diet and mental disorders

A 2015 viewpoint in The Lancet Psychiatry, written by members of the International Society for Nutritional Psychiatry Research, known as ISNPR, argued that diet is as important to psychiatry as it is to cardiology, endocrinology and gastroenterology. It called for diet and nutrition to be recognised as central determinants of physical and mental health. A viewpoint states its authors' position and is not a systematic review of the evidence.

A 2017 review in the Proceedings of the Nutrition Society, by authors from La Trobe University and Deakin University, gave an overview of the field. It stated that pharmacotherapy and psychotherapy avert less than half of the disease burden of mental illness, which the authors presented as a reason to look for additional strategies, and it described diet quality as a possible modifiable risk factor. The sources reviewed do not date the first use of the term nutritional psychiatry.

The society and its stated purposes

The ISNPR's rules, tabled for adoption at a society meeting on 17 December 2017, describe an incorporated not-for-profit association whose purposes are to support scientifically rigorous research into nutritional approaches to the prevention and treatment of mental disorders and their comorbidities. The listed purposes include building research collaborations, mentoring early-career researchers and supporting the translation of evidence into policy and clinical practice. Certifying practitioners is not among them.

Field, practice and supplement vocabulary

In the sources reviewed, nutritional psychiatry is used mainly as the name of a research field, in the title of a 2017 review and in the society's name. The 2015 viewpoint used the phrase nutritional medicine for the wider idea, covering both dietary quality and the selective use of nutrient-based supplements to address deficiencies or to augment other treatments. The terms describe research areas and not a single standardised treatment.

A 2022 guideline from a taskforce of the World Federation of Societies of Biological Psychiatry (WFSBP) and the Canadian Network for Mood and Anxiety Treatments (CANMAT) separates nutrient-based nutraceuticals from plant-based phytoceuticals. Its scope is supplements and plant products, so whole-diet approaches fall outside it. No protected professional title or training standard for nutritional psychiatry was found in the sources reviewed.

Dietary pattern labels

Research uses named dietary patterns and scores. A 2019 systematic review of observational studies pooled measures of adherence to the Mediterranean diet, the Healthy Eating Index and Alternative Healthy Eating Index, the Dietary Approaches to Stop Hypertension (DASH) diet and the Dietary Inflammatory Index. The SMILES trial's programme, called ModiMedDiet, was based on Australian and Greek dietary guidelines. Mediterranean-style in these studies therefore refers to the food groups in a given protocol and not to one fixed diet.

Programmes tested in trials

In the SMILES trial, adults with moderate to severe depression received seven individual consultations with a clinical dietitian over 12 weeks, in addition to their existing treatment. Sessions lasted about 60 minutes, the first four weekly and the last three fortnightly, and used motivational interviewing, goal-setting and mindful eating. Participants received a food hamper, recipes and meal plans, and the programme recommended no supplements. The control condition was a matched schedule of visits with trained personnel discussing neutral topics.

In HELFIMED, adults with self-reported depression were offered fortnightly food hampers and Mediterranean-style cooking workshops for three months, with fish oil supplements for six months. The comparison group attended fortnightly social groups for three months. The programme combined food, group teaching and a supplement, so its parts cannot be separated in the findings.

Supplement protocols

Supplement trials test a defined product and dose and not a dietary pattern. In a London pilot trial, adults with major depressive disorder who were taking an antidepressant but had an incomplete response received a multistrain probiotic at 8 billion colony-forming units a day, or placebo, for eight weeks. The 2022 guideline considered nutraceuticals mainly as adjuncts within standard medical or health-professional care.

Who delivers it

A survey completed by 40 mental health professionals at one Dutch institution, reported as a conference abstract, found that 65% of respondents regarded promoting healthy food as a key task and 65% said the topic had received insufficient attention in their training. About 62% reported adequate expertise to advise patients. These figures come from one institution and do not measure how the practice is delivered elsewhere. The sources reviewed describe no standard session structure outside research programmes.

Uses described by researchers and guideline authors

The 2015 viewpoint describes two kinds of use: improving diet quality, and selective use of nutrient-based supplements to address deficiencies or as monotherapy or augmentation. The 2017 review concentrates on depression and states that research is still needed in people with schizophrenia, bipolar disorder and anxiety disorders. These are stated aims of researchers within the field and are not evidence that the uses are effective.

The 2022 guideline graded individual nutraceuticals by condition. For unipolar depression it gave positive support, at varying levels, to adjunctive omega-3 fatty acids, adjunctive probiotics, adjunctive zinc, vitamin D, methylfolate and adjunctive S-adenosyl methionine, and it did not support several agents used alone. It also assessed bipolar disorder, obsessive-compulsive-related disorders, schizophrenia and attention-deficit/hyperactivity disorder, and found no nutraceutical with sufficient evidence in any anxiety-related disorder.

What the sources do not report

The sources reviewed do not report why people seek this approach or what commercial providers claim, and provider websites were not reviewed. A statement that a diet or supplement acts through gut bacteria, inflammation or neurotransmitter supply describes a proposed pathway. The 2017 review lists such pathways as possible mechanisms and does not treat them as established.

Dietary improvement for depression: two trials

SMILES was a 12-week, single-blind randomised trial of 67 adults with moderate to severe depression (33 diet, 34 social support), with complete data for 31 and 25 at 12 weeks. On the Montgomery-Åsberg Depression Rating Scale (MADRS), the diet group improved more (Cohen's d -1.16). Remission (MADRS below 10) occurred in 32.3% of the diet group (10 people) and 8.0% of controls (2 people), a number needed to treat of 4.1 (95% confidence interval 2.3 to 27.8).

HELFIMED recruited 152 adults with self-reported depression; 95 completed the three-month and 85 the six-month assessment. The Mediterranean-style group had a greater reduction in depression scores at three months (P = 0.03), and improvements were sustained at six months. Because depression was self-reported and fish oil was part of the package, the trial does not isolate the effect of food.

Pooled evidence on diet

A 2019 meta-analysis of randomised trials (searches to March 2018) included 16 trials with 45,826 participants, 15 of which studied nonclinical depression. Dietary interventions reduced depressive symptoms by a small amount (Hedges' g 0.162, 95% confidence interval 0.055 to 0.269). For anxiety (11 trials, 2,270 participants) no effect was found (g 0.085, confidence interval -0.031 to 0.202).

A 2019 systematic review of observational studies (searches to May 2018) found, among four longitudinal studies, a relative risk of incident depression of 0.67 (95% confidence interval 0.55 to 0.82) for highest against lowest Mediterranean diet adherence. This association does not show that changing diet prevents depression.

Supplements: omega-3, vitamin D and probiotics

A Cochrane review (searches to May 2015) of omega-3 fatty acids for adults with major depressive disorder included 26 trials, 25 against placebo. It found a small to modest benefit (standardised mean difference -0.32, 95% confidence interval -0.12 to -0.52; very low-quality evidence) that the authors considered unlikely to be clinically meaningful, and judged the evidence insufficient to determine effects.

A 2023 meta-analysis of 18 vitamin D trials in adults with depression found a small reduction in symptom scores (standardised mean difference -0.15, 95% confidence interval -0.26 to -0.04), with the effect reported only where baseline 25-hydroxyvitamin D exceeded 50 nmol/L. A pilot probiotic trial of 49 analysed adults reported greater improvement on some depression and anxiety scales, with wide confidence intervals and none on the GAD-7 anxiety scale.

Trial and review limits

Dietary trials cannot be fully blinded. SMILES acknowledged a small sample, a shortfall against its target and different dropout between arms, and used a comparison matched for visits. In the 2019 meta-analysis most trials involved nonclinical depression, so its pooled result does not describe people with a diagnosed depressive disorder. The follow-up periods above, up to six months, do not show longer-term effects.

Differing summaries of supplement evidence

The Cochrane omega-3 review rated the evidence low to very low quality and suggested an overestimate, while the 2022 guideline gave adjunctive omega-3 its strongest positive grading for unipolar depression. The guideline authors state that some meta-analyses they reviewed used heterogeneous studies with poor methodology and that isolated trials were not assessed. Only the abstract of the guideline was available for this draft.

Authorship, independence and mechanisms

Several sources cited here share authors from the field: the 2015 viewpoint was written by ISNPR members, and researchers at Deakin University appear on SMILES, the 2017 review and the 2019 meta-analysis. SMILES reports in-kind sponsorship from companies and author disclosures of pharmaceutical funding. These disclosures do not show bias, but much of the evidence is not independent of the field's proponents. A later analysis of the probiotic pilot trial found no between-group difference in inflammatory markers.

Adverse events reported in trials

SMILES reported no adverse events. In the Cochrane omega-3 review adverse events were similar between omega-3 and placebo groups, although the confidence interval included both a possible increase and a possible decrease and the evidence was of very low quality. The probiotic pilot trial reported no serious adverse reactions over eight weeks. These findings come from small or short trials and do not establish the safety of any product for all people.

Care boundaries and who was studied

The 2022 guideline judged the nutraceuticals reviewed to have acceptable safety and tolerability for low-risk over-the-counter use in most circumstances, and advised their use primarily as adjuncts within standard medical or health-professional care, especially in more severe mental illness. In SMILES, 55 of 67 participants were already using some therapy. The sources do not present dietary change as a replacement for prescribed treatment, and worsening mood or thoughts of self-harm need prompt professional assessment.

SMILES excluded people with bipolar disorder, pregnancy, severe food allergies, intolerances or aversions, and a current substance use disorder, so its findings should not be applied to those groups.

Eating disorders and food rules

SMILES did not list eating disorders among its exclusion criteria, and no intervention trial reviewed here reports results for people with eating disorders. A 2024 letter by eating disorder clinicians argues that the principle that all foods fit in every case should be reconsidered and that nutritional psychiatry be integrated into eating disorder treatment. It is an opinion piece, and it shows that handling of dietary change in this population is debated. The sources reviewed give no other guidance, so the question is one for specialist clinicians.

Training and regulation

No statutory regulation or protected professional title for nutritional psychiatry was found in the sources reviewed. The ISNPR is a research society and does not list practitioner certification among its purposes. The Dutch survey suggests nutrition training for mental health professionals may be limited. A reader can ask a practitioner which professional registration they hold, for example in psychiatry, medicine, dietetics or psychology, which differs by profession and country.